Materials such as silicon (Si) and gallium arsenide (GaAs) have found wide application in semiconductor devices for lower power and, in the case of Si, lower frequency applications. However, these more familiar semiconductor materials may not be well suited for higher power and/or high frequency applications, for example, due to their relatively small bandgaps (e.g., 1.12 eV for Si and 1.42 for GaAs at room temperature) and/or relatively small breakdown voltages.
In light of the difficulties presented by Si and GaAs, wide bandgap semiconductor materials, such as silicon carbide (2.996 eV for alpha SiC at room temperature), and the Group III nitrides, including gallium nitride (e.g., 3.36 eV for GaN at room temperature), have been considered for use in high power, high temperature and/or high frequency applications and devices. These materials, typically, may have higher electric field breakdown strengths and higher electron saturation velocities as compared to gallium arsenide and/or silicon.
Ion implantation is a method for impurity doping in semiconductors where precise control of doping level and/or doping uniformity may be desired. A conventional ion implantation system may include an ion source configured to generate a desired implant ion species by ionization of a corresponding element, an acceleration tube configured to accelerate the ion species to a desired kinetic energy, a mass separator magnet and beam splitter configured to isolate a desired ion species, and a target chamber where the ion species may be directed to a surface of a semiconductor wafer. For example, a conventional Group-III nitride substrate, such as gallium nitride (GaN), may be doped with silicon to improve conductivity therein.
A common problem in conventional ion implantation may involve contamination in the implant region of the semiconductor wafer. For example, a foreign species or implant contaminant with the same particle weight as that of the desired implant species may be implanted along with the desired implant species in the ion implantation process. The implant contaminant may, for example, be present as a residual coating on the inner walls of the ion source chamber, and may be released due to heat used during the ionization process. As such, particles of the implant contaminant may be implanted into the substrate in place of the desired ion species, thereby reducing the desired ion concentration of the implant region. Moreover, because conventional mass spectrometry may be used to detect implant concentration based on particle weight, it may be difficult to determine the presence of implant contaminants in the substrate, and thus, the actual concentration of the desired ions in the implanted region. Accordingly, device performance may be detrimentally affected.